This disclosure relates to variable stator vanes and their components with respect to flowpath case structure.
Latest aircraft requirements have created challenges for the jet engine manufacturers. In order to meet these requirements, jet engines are incorporating adjustable features to enable variable cycle engines. One example is variable vanes in the turbine section, which could move (rotate) to vary the flow area of the turbine.
Variable Area Turbines (VATs) are an adaptive component which, when coupled with other adaptive engine features such as adaptive fans, compressors with variable vanes, variable nozzles, etc. can yield significant benefits in overall gas turbine engine performance. Such benefits may include but are not limited to reduced specific fuel consumption (SFC), reduced high pressure compressor discharge air temperature at take-off conditions, improved throttle response, and improved part life.
The VATs function is to provide a change in the turbine flow parameter by changing turbine flow area, for example. Varying turbine flow area may be achieved by rotating a plurality of the individual vane airfoils in a first stage of the turbine. In order to minimize turbine vane performance debits associated with rotating the variable vane airfoil, measures should be taken to minimize the areas of concern. These areas include, for example, varying cooling flow requirements, leakage flow, and variable vane hardware gaps. One of the critical variable vane hardware gaps that should be minimized is the gap between a rotating variable vane endwall and the inner and outer diameter flowpaths. Minimizing this gap will help reduce the amount of hot gas that can pass from the pressure side to the suction side of the vane airfoil, thus improving turbine performance and the durability of the variable vane airfoil itself.
In one example configuration, the variable vane is rotated within a cylindrical inner and outer diameter flowpath. During rotation the variable vane endwall gaps change. When the variable vane airfoil is rotated from a nominal position, the gap between the vane outer diameter endwall edges and the outer diameter flowpath surfaces decreases. To avoid clashing, the variable vane nominal endwall gap at the outer diameter must be increased. However, increasing this gap can result in an increase in the hot gas migration under the vane endwalls from the pressure side to the suction side of the variable vane, reducing turbine performance and airfoil durability.
Further, as the variable vane is rotated from the nominal position the gap between the vane inner diameter endwall edges and the inner diameter flowpath increases. Increasing this gap can also result in an increase in the hot gas migration under the vane endwalls from the pressure side to the suction side of the vane. These adverse effects are even more severe for a vane that rotates within conical inner and/or outer diameter flowpaths.